Method and apparatus for annealing strip



3 Sheets-Sheet `1.l

J. D. KELLER METHOD AND APPARATUS JFOR 'ANNEALING STRIP Filed June 2o, 1959 \M \\\\\\\\\\\\\\\\\\\\\\\\\\\W\\ \\\\\\\\\\\\\\\\\\\\\\\\\W\9\\ Feb. 13,.I A1,941.V I

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Patented Feb. 18, 1941 UNITED STATES 2,232,391 METHD AND APPARATUS FOR ANNEALING STRIP l John n. neuer, Pittsburgh, n.

Application June 20, 1939, Serial No. 280,117

6 Claims. This invention' relates to the processing of flat rolled metal stock and,` in particular tothe annealing of cold rolled steel strip.

The annealing of ferrous strip has been carriecl on heretofore by placing the materialin the form of either coils or sheets. within a protective cover, heating it to the desired temperature and subsequently permitting it to coolslowly. The

time required by this process is considerable so that the cost of the necessary apparatus, per ton of hourly or daily capacity, is quite high. A further objection is that all portions of the coil or stack, are not heated to precisely the same temperature whereby the material lacks uniformity after processing.

I have invented a novel method and apparatus for annealing strip which overcome the aforementioned objections by 'providing equipment that can be installed at relatively low cost, for heating and .cooling the material in single thickness or strand form, whereby the time required for completely processing a given length of strip is greatly reduced as compared to that which has been necessary heretofore.

In a preferred embodiment, the apparatus of my invention comprises heating and cooling chambers provided with means for conducting strip therethrough successively in 7strand form. These means are preferably in the form of rollers between which the strip is looped back and forth for continuous movement through the chambers. I also provide means for circulating gas through the chambers to heat and cool the strip passing therethrough, respectively. Heat-exchangers disposed adjacent the chambers alter the temperature of the gas entering the chambers so that the desired heating or cooling takes place therein.

The following detailed description of a -preferred embodiment of the apparatus refers to the accompanying drawings in which Fig. 1 is a longitudinal, vertical, central section through the heating and cooling chambers with parts thereof shown in elevation; l

Fig. 2 is asectional view taken substantially along the plane of line lI-II of Fig. 1; line I-I of Fig. 2 indicates the plane on which the section of Fig. 1 is taken; Y

Fig. 3 is a side elevation such as'would be seen by loolringv from the top of Fig. 2, partly in section and partly broken away: andv l Fig. 4 is a partial view similar to Fig. 1 showing a modification.

Referring now in detail to the drawings, heating andcooling chambers Il and Il are so disposed relative to each other as to facilitate the passage of strip from one to the other. The chambers Il and Il are preferably constructed of refractory insulating bricky assembled within an enclosure composed of sheathing plates l2 and suitable frame members (not shown). Bames I3 and Il extend inwardly from opposite sides 'of the heating chamber for a purpose which will appear shortly. Guide rollers I5 are journaled adjacent the top and bottom of the chamber Ill and are so disposed as toconvey a strip I6 trained therearound, continuously through the chamber,

each point on the strip traversing a plurality of loops as it` advances through the chamber.. f The rollers I5 are .journaled in suitable bearings v(not shown) which may conveniently be supported on the framework of the enclosure for the chamber l0. If desired, means may be provided for driving all or some of the rollers I5.

An entrance slot I'I adjacent one endof the chamber permits the strip I0 to be drawn around a guide roller Il and thence around the rollers II. Bames I9 of suitable shape which may conveniently be composed of sheet metal having the necessary resistance to high" temperatures, extend between the rollers at the top andbottomof the chamber and are supported on bars 20 extending therethrough and embedded in the chamber walls. As clearly shown in Fig, 1, the bames I9 define narrow passages for the runs of the strip between .opposed rollers II.

The cooling chamber Il is similar in construcv tion and arrangement tothe heating' chamber III and a detailed description thereof is unnecessary for that reason, the' elements of the cooling chamber being indicated by the numerals apchamber with a prime affixed. Asshown in Fig. 1, the heating andcoollng chambers are connected by a passage 2i. After `traversing both the heating and .cooling chambers, the'- strip o emerges through a slot Il' atl the end of the latter and passes arounda guide miler I8 to a coiler or other take-up meanshi. e., pinch rolls or the charges through adivergingv connection into an inlet 24a formed in the side of the heating chamber I0. The heat-exchanger Mmay be of any l suitable type sov long as it' prevents contaminaplied to corresponding elements of the heating tion of the atmosphere of the chambers by combustion gases, but in the embodiment illustrated it is of the surface type and includes a plurality of vertically extending heat-exchange tubes 21. A burner 21a adjacent the lower ends of the tubes 21 supplies hot combustion gases to the interior thereof, thereby heating them. It will be apparent that the gas composing the atmosphere in the heating chambers I 0 and II will be circulated in the direction of the arrows and heated on passing through the bank ofl tubes 21 composing the heat-exchanger 24.

A passage 28 connects opposite ends of the heating and cooling chambers. A heat-exchanger 29 is disposed in the passage adjacent the en- ,y

trance to the chamber II. This exchanger may also be of any suitable type, but as illustrated, comprises a plurality of tubes between which the gas passes prior to entering the cooling chamber. Cooling uid of any desired type is circulated through the tubes 29 by appropriate means.

In operation, the apparatus shown serves to heat the strip I6 'progressively to the desired temperature and then cool it by convection.v The strip may conveniently be fed into the apparatus from a coil supported in an uncoiler or the like. The chambers I0 and II are provided with removable wall sections (not shown) .to permit a strip to be initially trained around the rollers I5 and between the baiiles I9. After threading the first strip, succeeding coils will Vbe secured together asby welding, stitching or the like, so that a continuous passage of the strip through the apparatus is obtained without the necessity of rethreading.

A protective atmosphere is maintained within the chambers I0 and II, being supplied thereto by appropriate connections from a suitable source of non-oxidizing gas. I

t The heat-exchanger 24 is preferably operated in such manner that the gas entering the inlet 24a is at a temperature of about 1350 F. This gas passes between the baliies I9 and around the bailies I3 and I4- and Athus has repeated intimate contact with the runs of strip between opposed rollers I5. The bailles I3 and I4 cause all the gas delivered to the heating chamber to make several complete passes across the multiple loops in which the strip is supported in the chamber. The baffles I9 prevent the gas from passing between adjacent runsl Without having intimate contact therewith.

The strip entering the heating chamber and advancing progressively therethrough is gradually raised to the temperature of the gases entering the chamber. I utilize the counter-current principle by causing the gas at its maximum temperature to impinge on the strip at the maximum temperature of the latter. The gas, after losing some of its heat to the strip on the rst pass through the multiple runs, has repeated contact therewith on successive passes and imping'es on the cold entering strip after the gas temperature has been somewhat reduced.

After the gas has made the several passes through the runs of strip in the heating chamber and lost most of its heat, it ows through the passage 28 and is further cooled by the heatexchanger 29. 'I'he cooled gas then makes repeated passes through the runs of strip supported in the cooling chamber II before returning to the blower 23. As in the heating chamber, the counter-current principle is utilized by causing the gas at its minimumV temperature to engage the strip which is at the minimum temperature. A portion of the heat absorbed by the strip as it passes through the heating chamber is thus recovered therefrom by the gas impinging thereon in the cooling chamber so that af-ter the apparatus has been operating a short while, only a relatively small amount of heat will be required to make up for that lost through the furnace walls and to the heat-exchanger 29.

After beingheated to the desired temperature 1n the heating chamber, thev strip is cooled in the cooling chamber by the repeated contact of the V gas forming the atmosphere within the chambers vpass of the heating and cooling chambers may varyfrom the arrangement shown in the drawings. Each pass, furthermore, may be divided by one or more horizontal partitions to cause the gas to flow back and forth repeatedly through each pass before entering the next one.

Fig. 4, wherein the gas enters the heating chamber at 35, ows upwardly around baiiles I9, around a bailie 36 and downwardly around further baiiles I9, and so on. This construction differs from that of Figs. 1 to 3 in that the several passes of the gas through the heating and cooling chambers take place along substantially vertical paths, instead of transversely along substantially horizontal paths. In the modified construction, the inlet to the heating chamber is near the bottom or top thereof as shown.

As will be apparent from the foregoing description and explanation, the invention provides a simple yet effective method and apparatus for continuously annealing strip. Since the material is heated and cooled in single thickness or strand form, it is rapidly raised to the desired temperature and cooled therefrom. A relatively Alarge hourly or daily capacity is thus obtained and the cost of the apparatus per unit of capacity is much lower than that of conventional annealing apparatus. The fuel cost is also reduced since a portion of the heat initially absorbed by the strip is recovered therefrom in the cooling stage. The entire apparatus is made gas-.tight by suitably welding the sheathing plates I2 and a slight positive pressure is maintained on the gas within the chambers I0 and II to prevent the infiltration of the atmosphere. Since the slots I'I and I1' must be kept open, this means that the supply of non-oxidizing atmosphere to the chambers must be continuous. The heat-exchanger may, if desired, be enclosed within the refractory walls of lthe furnace. l

The rollers may be providedvwith scrapers and their surfaces vmay be either highly polished nickel chromium alloy or similar metal to which the metal of the strip has little tendency to adhere, or a softer material such as copper or Mone] metal.

Although I have illustrated and described but a preferred embodiment and practice of the invention, it will be recognized that changes in the apparatus and procedure disclosed may be made withoutl departing from the spirit of the invention or the scope of the appended claims.

I claim:

`l. Apparatus for annealing strip comprising heating and cooling chambers, means for con- A modified arrangement of passes is shown in* ,25

:sesv

so V

ducting strip successively therethrough, means for circulating gases through said chambers successively, and a heater having heat-exchange surfaces for heating the gases. said means and said heater` being so positioned and connected to said chambers that the gases are withdrawn from the cooling chamber and pass through the heater prior tol entering the heating chamber, said heater being adapted to prevent contamination of the circulating gases by extraneous gases.

2. In a method of annealing strip, the steps including passing strip in strand form continuously through a chamber, looping the strip up and down in said chamber while advancing it generally along a predetermined path, circulating gas repeatedly in a generally horizontal direction across said path, and bringing the gas into contact with heat-exchange surfaces prior to its'entry into said chamber, thereby heating the strip to a substantially uniform temperature across its width, substantially solely. by convection in its passage through the chamber.

3. Annealing apparatus' including a chamber, means including spaced rolls for looping strip back and forth in said chamber and conducting it progressively therethrough in strandform, a heater adjacent said chamber having heat-exchange surfaces for heating gas, and means for circulating gas through said heater and chamber to heat'the strip to annealing temperature substantially solely by`convection, said heater being so constructed and arranged as to prevent contamination of the gases circulating therethrough.

byextraneous gases.

4. Annealing apparatus including a chamber. parallel rollers disposed in said chamber in spaced relation and near the top and bottom thereof, over which strip is adapted to travel` back and forth in loops and be thereby conveyed progressively therethrough, gas-heating means aasasei temperature substantially solely'by convection vfor circulating gas through said heating means and chamber to heatthe strip to annealing temperature substantially solely by convection, and

a substantially vertical baille wall extending substantially'the full height of said chamber and from one sidethereoi across substantially the Vfull width thereof between adjacent loops toward the other, but terminating short of the other side thereby causing the gas to make a plurality'of generally horizontal passes transversely through a plurality of adjacent loops of strip.

6. Annealing apparatus including a chamber, rollers disposed in said chamber in vertically spaced relation adapted to convey strip up and down therein and 'progressively therethrough, substantially vertical baille walls `extending from both sides of the chamber and across substantially the full width thereof between adjacent strands of spaced loops of strip but terminating short of the other side, gas-heating means ad' jacent said chamber, and means for circulating gas through said gas-heating means and around the baille walls in the chamber whereby to sub- 3 n adjacent said chamber having heat-exchange i ject the strip to a plurality or horizontal transverse passes by said gas and heat it to annealing JOHN D. KELLER. 

